Women without contraceptives will be examined in the luteal phase (i.e. in the two weeks before menstruation). The ambulant registry will be done continuously during one week with so called i-Buttons (IButtonTM, Maxim, USA). These will be fixed to various parts of the body (i.e. wrist, ankle, …) with Fixomull, a medical bond. Also the subjects have to wear a instrument for registration activity, the so called Actiwatch (Cambridge, UK). The data that will be gained from these instruments, shall help us to objectify sleep-latency and sleep-fragmentation ("sleeping-through").